• Thank You

    Thanks to your fundraising efforts, the 23rd annual Canadian Breast Cancer Foundation CIBC Run for the Cure raised $25 million across Canada for breast cancer research, education and advocacy programs.

  • Calling all foodies

    Register today for the chance to meet, learn from and compete alongside celebrity chefs in the ultimate culinary challenge in support of CBCF

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  • Give Pink this October!

    Check out the organizations that for the month of October will be donating a portion of proceeds to Canadian Breast Cancer Foundation – Ontario Region!

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  • Shoppers Drug Mart National Gala

    Book your date with beauty. On Nov. 8, Shoppers Drug Mart stores across the province will support CBCF during their Holiday Beauty Gala

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  • National Grants Competition

    The Canadian Breast Cancer Foundation is pleased to announce the launch of a new national research competition, Stand Up To Cancer Canada - Canadian Breast Cancer Foundation Breast Cancer Dream Team, supported by CIBC.

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  • 1/3 of breast cancers can be prevented

    Learn ten other surprising facts about breast health and build your personal plan for living well.

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  • Ontario Region Report to the Community

    The 2014 interactive Report to the Community is now available. Find in-depth information, stories, videos and more.

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  • Research Saves Lives

    Continued support allows the Foundation to play a vital role in internationally acclaimed, groundbreaking research discoveries in the areas of prevention, diagnosis, treatment and care.

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Pregnancy and Breastfeeding

There are several stages in a woman’s reproductive life that influence her risk of developing breast cancer. These stages can increase or decrease that risk in different ways.

A woman’s life stages are related to hormonal changes that occur naturally, such as when you start and stop menstruating if or when you become pregnant and carry the pregnancy to full term, and if or when you are able to breastfeed.

There is evidence that pregnancy and childbirth influence your risk of breast cancer. Women who do not have children have a low increase in the risk of developing breast cancer compared to women who have had a child before the age of 35.

Pregnancy and reduced breast cancer risk

Research shows that the risk of breast cancer is reduced in women who have had children, particularly if they gave birth before the age of 30. Having more than one child also decreases your breast cancer risk and with every subsequent child your risk decreases further.

The hormones involved in a pregnancy carried to full-term mature the breast tissue in a way that seems to protect against breast cancer.  

Pregnancy and increased breast cancer risk

Like women who have no children, women who have their first child at the age of 35 or older have a low increase in the risk of developing breast cancer.

There is also a short-term increase in the risk of developing breast cancer after childbirth. This period of increased risk may last for up to several years following the birth of your child, and is likely a result of hormonal changes that promote cell growth in breast tissue.

Breastfeeding offers protective benefits for the mother

If breastfeeding is an option for you and your baby, evidence suggests that it can reduce your risk of developing breast cancer. 

The biggest benefits are from longer periods of breastfeeding, for a year or more with one child or over several births. The effect of breastfeeding on breast cancer risk may be related to the fact that women usually stop menstruating while they are still breastfeeding: this lowers a woman’s total number of menstrual periods over her life. Fewer menstrual periods means less exposure to estrogen. Breast tissue is susceptible to the effects of estrogen and estrogen exposure plays a role in the development of breast cancer.

The Canadian Breast Cancer Foundation encourages you to learn about your breast health, breast cancer risk, ways to reduce your risk, and the benefits and limitations of screening for the earlier detection of breast cancer. To inform your decisions, we also encourage you to consider speaking to a health care provider.

Established risk factors 

Non-modifiable Risk Factors Modifiable Risk Factors

Gender and age

Body weight

Personal cancer history

Physical activity

Family cancer history and genetics

Alcohol use

Early menstruation and late menopause


Breast density

Exposure to hormones: the Pill, IVF, and HRT

Breast conditions

Pregnancy and breastfeeding


Radiation exposure


Canadian Breast Cancer Foundation – Ontario Region. (2010). Earlier Detection and Diagnosis of Breast Cancer: A Report from It’s About Time! A Consensus Conference. 

National Cancer Institute (US). Pregnancy and Breast Cancer Risk.  Accessed July 31, 2011.

Collaborative Group on Hormonal Factors in Breast Cancer. (2002). Breast cancer and breastfeeding. In The Lancet, Vol. 360, No. 9328. Accessed July 31, 2011.